"We were surprised to learn about the reference to Windows 8 in this notice," a company spokesperson said. "Microsoft has been working proactively... to ensure that our products and services meet all government procurement requirements."

The Chinese embassy in the United States did not immediately provide comment.

The more likely reason, some suspect, is that China may be trying to avoid getting stuck with outdated Windows systems in the future. Windows operating systems are huge in China, and now that Microsoft has ended support for Windows XP, the Chinese government finds itself in a tough spot. Nearly three-quarters of Chinese PCs are running XP, according to NetMarketShare. That leaves tens of millions of computers there at risk of bugs and malware.

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This isn't the first time Microsoft faces challenges in China. The government's long-running ban on foreign gaming consoles has kept out Microsoft's Xbox ever since it launched in 2001. China lifted that ban late last year.

Microsoft is also fighting an ongoing piracy battle in China. The company estimates 90% of Chinese PCs are running illegal copies of Windows software.